The empty string is usually represented similarly to other strings. Some languages treat some or all of the following in similar ways: empty strings, null references, the integer 0, the floating point number 0, the Boolean value false, the ASCII character NUL, or other such values. The empty string is a legitimate string, upon which most string operations should work. In most programming languages, the empty string is distinct from a null reference (or null pointer) because a null reference points to no string at all, not even the empty string. However, a string comparison function would indicate that all of these empty strings are equal to each other.Įven a string of length zero can require memory to store it, depending on the format being used. In this way, there could be multiple empty strings in memory, in contrast with the formal theory definition, for which there is only one possible empty string. Thus, the same string (for example, the empty string) may be stored in two or more places in memory. Strings are typically stored at distinct memory addresses (locations). In most programming languages, strings are a data type. In context-free grammars, a production rule that allows a symbol to produce the empty string is known as an ε-production, and the symbol is said to be 'nullable'. The empty string precedes any other string under lexicographical order, because it is the shortest of all strings.Reversal of the empty string produces the empty string. The set of all strings forms a free monoid with respect to ⋅ and ε.

The empty string is the identity element of the concatenation operation. a set of strings) that contains no strings, not even the empty string. The empty string should not be confused with the empty language ∅, which is a formal language (i.e.

In formal treatments, the empty string is denoted with ε or sometimes Λ or λ. There is only one empty string, because two strings are only different if they have different lengths or a different sequence of symbols. The empty string is the special case where the sequence has length zero, so there are no symbols in the string.

Formally, a string is a finite, ordered sequence of characters such as letters, digits or spaces.

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